Electronic structure of cubic ErxGa1−xN using the LSDA+U approach

Electronic structure calculations were performed for substitutional erbium rare-earth impurity in cubic GaN using density-functional theory calculations within the LSDA+U approach (local spin-density approximation with Hubbard-U corrections). The LSDA+U method is applied to the rare-earth 4f states. The Er_xGa_1−xN is found to be a semiconductor, where the filled f-states are located in the valence bands and the empty ones above the conduction band edge. The filled and empty f-states are also shown to shift downwards and upwards in the valence and conduction bands, respectively, with increase in the U potentials.     

Ab initio study of the structural,electronic, elastic and magnetic properties of Cu2GdIn,Ag2GdIn and Au2GdIn

We preformed first-principle calculations for the structural, electronic, elastic and magnetic properties of Cu₂GdIn, Ag₂GdIn and Au₂GdIn using the full-potential linearized augmented plane wave (FP-LAPW) scheme within the generalized gradient approximation by Wu and Cohen (GGA-WC), GGA+U, the local spin density approximation (LSDA) and LSDA+U. The lattice parameters, the bulk modulus and its pressure derivative and the elastic constants were determined. Also, we present the band structures and the densities of states. The electronic structures of the ferromagnetic configuration for Heusler compounds (X₂GdIn) have a metallic character. The magnetic moments were mostly contributed by the rare-earth Gd 4f ion.     

First-principles linear muffin-tin orbital investigations in the electronic and magnetic structures of double perovskites Ba2TMoO6 (T=V,Cr, Mn,Fe and Co)

The electronic and magnetic structures of ordered double perovskites Ba₂TMoO₆ (T=V, Cr, Mn, Fe and Co) are systematically investigated by means of the first-principle linear muffin-tin orbitals with the atomic-sphere approximation (LMTO-ASA) method. The calculations are performed by using the both local spin density approximation (LSDA) and the LSDA+U Coulomb interaction schemes. The results show a half-metallic ferrimagnetic ground states for T=Cr, Fe and Co in LSDA+U treatment, whereas half-metallic ferromagnetic character is observed for T=V. For T=Mn, insulating ground state is obtained, stabilized in the antiferromagnetic state. The LSDA+U calculations yield better agreement with the theoretical and the experimental results than do the LSDA.     

Optical spectroscopy and electronic structure of the Er5Ge3 compound

The results of the study of the optical properties and electronic structure of the Er₅Ge₃ compound have been presented. In the wavelength range of 0.22–15 μm (0.083–5.64 eV), the optical constants have been measured, and the spectral and electronic characteristics have been determined. The spin-polarization calculations of the band spectrum have been performed in the local electron spin density approximation (LSDA) with a correction for strong correlations in the 4f shell of the rare-earth atom (LSDA + U method). The main features of the experimental dispersion dependence of the optical conductivity in the region of quantum light absorption have been interpreted based on the results of calculations of the electron density of states.     

B-cation effect on the electronic and magnetic properties of CeBO3 (B=Ga, In) compounds from first principles study

The ab initio APW+lo method is used to study the cation effect on the electronic structure of CeBO₃ (B=Ga, In) compounds. High-pressure structural behavior, magnetic phase stabilities and electronic properties of both materials have been investigated. The observed most stable phases are the orthorhombic (Pnma) and hexagonal (P6₃cm) for CeGaO₃ and CeInO₃, respectively. It is shown that the ferromagnetic (FM) state in CeGaO₃ is energetically more favorable than the anti-ferromagnetic (AFM) one, unlike CeInO₃ where the AFM-III configuration is the lowest in energy. LSDA+U calculation shows that the valence band maximum is located at T point and the conduction band minimum is located at the center of the Brillouin zone, resulting in a wide indirect energy band gap of about 3.6 eV in the ferromagnetic ordering CeGaO₃ which is typical of semiconductor with large gap. CeInO₃ compound keeps the metallic character using DFT+U calculation.     

Effect of Si substitution on electronic structure and magnetic properties of Heusler compounds Co2TiAl1−xSix

The electronic structures of Co-based Heusler compounds CoTiAl_1−xSi_x (x=0, 0.25, 0.5, 0.75 and 1) are calculated by first-principles using the full potential linearized augmented plane wave (FP-LAPW) method within GGA and LSDA+U scheme. Particular emphasis was put on the role of the main group elements. In recent years, the GGA calculations of Co₂TiAl (x=0) and Co₂TiSi (x=1) indicated that they are half-metallic, but the electronic structure of this compound with x=0.25, 0.5 and 0.75 has not been reported yet, neither theoretically nor experimentally. The calculated results reveal that these are half-metallic and exhibit an energy gap in the minority spin state and also show 100% spin polarization. The substitution of Al by Si leads to an increase in the number of valence electrons, with increasing x. Our calculated results clearly show that with the Si doping, the lattice parameter linearly decreases; bulk modulus increases, and the total magnetic moment increases. The calculated energy gap in the minority spin state, using GGA scheme, was smaller than that obtained by using LSDA+U scheme. The outcomes of this research also show that the Co-3d DOS and therefore, the magnetic properties of compounds are dependent on electron concentration of the main group elements and it will affect the degree of p-d orbital occupation.     

Electronic and magnetic properties of NdCrSb3: A first principles study

The electronic and magnetic properties of NdCrSb₃ are calculated by the first principles full-potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). Density of states (DOS), magnetic moments and band structures of the system are presented. For the exchange and correlation energy, local spin density approximation (LSDA+U) with the inclusion of Hubbard potential U is used. Our calculation shows that the 3d state electron of Cr and 4f state electrons of Nd contribute to the total DOS and the band structures. The effective magnetic moment is found to be 5.77μ_B, which is comparable to the earlier experimental results of NdCrSb₃.     

Properties of hexagonal Al2Ge2RE (RE=Y,La,Ce,Nd,Eu,Gd,Tb,Y b and Lu) : A first-principles study

In this work, we present a study of the structural, elastic and electronic properties of the Al₂Ge₂RE (RE=Y, La, Ce, Nd, Eu, Gd, Tb, Yb and Lu) through the approaches of generalized gradient approximation (GGA) and local spin density approximation with the Hubbard energy (LSDA+U) based on density-functional theory. For most of the compounds (RE=Y, La, Ce, Nd, Eu, Yb and Lu), the results of the structural constants calculated from the approach of LSDA+U are in good agreement with the reported experimental data. Both the approaches of GGA and LSDA+U have been used to calculate DOS. Compared with the results of the GGA approach, the LSDA+U is more credible because it can show the influence of RE-f states and the RE-f states play an important role in the compound. The magnetic property has been investigated according to the result of DOS and it shows that the Al₂Ge₂Y, Al₂Ge₂La, Al₂Ge₂Y b and Al₂Ge₂Lu do not exhibit obvious magnetic property, while the other five ternary compounds are magnetic. The Voigt-Reuss-Hill (VRH) approach is used to calculate the elastic properties including bulk and shear moduli. The results of the calculated Poisson’s ratio ν and the B/G ratio demonstrate that all the Al₂Ge₂RE ternary compounds are brittle materials. The compounds, i.e. Al₂Ge₂Nd, Al₂Ge₂Eu, Al₂Ge₂Gd and Al₂Ge₂Tb which are mechanically unstable, display differences with the other five in the elastic properties.     

A full potential all-electron calculation on electronic structure of NiO

We perform a first principle calculation on NiO system, a prototypical correlated electronic system due to partial filled 3d electronic shell, using various density functional theory (DFT) and hybrid functional methods inclusion of spin polarization (SP), on-site Coulomb repulsion U and spin–orbit coupling (SOC) effects. It is shown that localized spin density approximation (LSDA) plus U (LSDA?+?U) correctly reproduce experimental lattice parameter, while spin polarization generalized gradient approximation (SP?+?GGA?+?U) obviously overestimates lattice parameter. LSDA?+?U/SP?+?GGA?+?U band gaps and magnetic moments are in agreement with experimental data, and correctly predict NiO to be an insulator. NiO undergoes a Mott–Hubbard metal–insulator transition (MIT) by addition of Coulomb interaction U. Our LSDA?+?SOC calculation shows that SOC further splitting of Ni d e_g and t_2g orbitals into d_z2, d_xy, d_x2y2 and d_xz?+?d_yz orbitals, and SP nearly cancels out SOC effect, giving rise to symmetry of density of states (DOS) for spin-up and spin-down states, hence appearance of zero net magnetic moment. For LSDA?+?U?+?SOC calculation, combination effect of SP, U and SOC results in non-occupying of spin-up conduction band and a negligible density of states for spin-down states.     

First-principles investigations of Cr doping effects on electronic structure and magnetic properties in Sr2FeReO6

The electronic structures and magnetic properties of double perovskites Sr₂Fe_1−xCr_xReO₆ (x=0.0, 0.25, 0.5, 0.75, 1.0) have been studied within the local spin density approximation (LSDA) and LSDA+U schemes. The calculated results reveal that with increasing Cr content the cell volume shrinks 2.61%; the Fe/Cr site magnetic moment decreases while the Re-site moment increases. The total spin magnetic moment linearly decreases with the Cr doping from 3.00μB for x=0.00 down to 1.00μB for x=1.00 per formula unit. The magnetic coupling constants increase with increasing x. The electronic structure calculations indicate that the electronic concentration in the Re spin-down subband slightly increases resulting from the increase of bonding-antibonding interaction between the localised and the delocalised states in spin-down band; the coupling of O-2p_↑ and transition-metal-3d_↑ is substantially enhanced with the Cr doping. We discuss the origin of the anomalously high TC of Cr-doped Sr₂FeReO₆ compounds in terms of band hybridization effects.     

Spin-polarized structural, electronic and magnetic properties of diluted magnetic semiconductors Cd1−xMnxTe in zinc blende phase

We have investigated the structural, electronic and magnetic properties of the diluted magnetic semiconductor (DMS) Cd_1−xMn_xTe (for x=0.75 and 1.0) in the zinc blende (B3) phase by employing the ab-initio method. Calculations were performed by using the full potential linearized augmented plane wave plus local orbitals (FP-L/APW+lo) method within the frame work of spin-polarized density functional theory (SP-DFT). The electronic exchange-correlation energy is described by generalized gradient approximation (GGA). We have calculated the lattice parameters, bulk modulii and the first pressure derivatives of the bulk modulii, spin-polarized band structures, and total and local densities of states. We estimated the spin-exchange splitting energies Δ_x(d) and Δ_x(pd) produced by the Mn3d states, and we found that the effective potential for the minority spin is more attractive than that of the majority spin. We determine the s-d exchange constant N₀α (conduction band) and p-d exchange constant N₀β (valence band) and these somewhat agree with a typical magneto-optical experiment. The value of calculated magnetic moment per Mn impurity atom is found to be 4.08 μ_B for Cd_0.25Mn_0.75Te and 4.09 μ_B for Cd_0.0Mn_1.0Te. Moreover, we found that p-d hybridization reduces the local magnetic moment of Mn from its free space charge value of 5.0 μ_B and produces small local magnetic moments on the nonmagnetic Cd and Te sites.     

Electronic structure and optical properties of TbNi5−xCux

In this paper we present theoretical investigation of optical conductivity for intermetallic TbNi_5−xCu_x series. Within the framework of LSDA+U calculations, electronic structure for x=0, 1, 2 is calculated and additionally optical conductivity is obtained. Disorder effects of Cu for Ni substitution on a level of LSDA+U densities of states (DOS) are taken into account via averaging over all possible Cu ion positions in the unit cell for given doping level x. Gradual smoothing of optical conductivity structure at 2 eV together with simultaneous intensity growth at 4 eV corresponds to increase of Cu and decrease of Ni content.     

A comparative study of a Heusler alloy Co2FeGe using LSDA and LSDA+U

We have calculated the on-site Coulomb repulsion (U) for the transition elements Co and Fe. To study the impact of Hubbard potential or on-site Coulomb repulsion (U) on structural and electronic properties the calculated values of U were added on GGA and LSDA. We performed the structure optimization of Co₂FeGe based on the generalized gradient approximation (GGA and GGA+U). The calculation of electronic structure was based on the full potential linear augmented plane wave (FP-LAPW) method and local spin density approximation (LSDA) as well as exchange correlation LSDA+U. The Heusler alloy Co₂FeGe fails to give the half-metallic ferromagnetism (HMF) when treated with LSDA. The LSDA+U gives a good result to prove that Co₂FeGe is a HMF with a large gap of 1.10 eV and the Fermi energy (E_F) lies at the middle of the gap of minority spin. The calculated density of states (DOS) and band structure show that Co₂FeGe is a HMF when treated with LSDA+U.     

The ground states properties and the spin effect on the cubic and hexagonal perovskite manganese oxide BaMnO3: GGA+U calculation

Particularly interesting as candidates to technological applications are the manganese perovskites with AMnO₃ formula. Their magnetic structure was described as resulting from a particular ordering of the occupied d orbitals which possess. This reflects my understanding of the structural, electronic and magnetic phenomena, which is well established only in the limit where the systems show localized or itinerant electron behavior. In general, the perovskites of ABO₃-type are well known with their (anti)ferroelectric, piezoelectric and (anti)ferromagnetism properties applied in considerable technological investigations. In my paper, I studied the ground states properties of the BaMnO₃ perovskite oxide. My structural properties are given using LSDA, GGA, LSDA+U and GGA+U in the aim to introduce the exchange correlation potential. In the following paper, I use the GGA+U on the electronic and magnetic properties calculation. I show in my study the density of states, the band structures and also the charge density figures. My results such as lattice parameter, bulk modulus and its pressure derivative agree very well with available theoretical works and experimental data. I discuss the magnetic moment and the U-Hubbard effect introduced by LSDA+U and GGA+U on my results given in this paper.     

Study on the ground state of NiO: The LSDA (GGA)+U method

The ground-state properties of NiO have been investigated using the all-electron full-potential linearized augmented plane wave (FLAPW) and the so-called LSDA (GGA)+U (LSDA—local-spin-density approximation; GGA—generalized gradient approximation) method. The calculated result indicates that our estimation of U is in good agreement with experimental data. It is also found that none of the LSDA (GGA) methods is able to provide, at the same time, accurate electronic and structural properties of NiO. Although the GGA+U method can properly predict the electronic band gap, it overestimates the lattice constant and underestimates the bulk modulus. Then only the LSDA+U method accurately reports the electronic and structural properties of NiO. The calculated band gap and the density of states (DOS) show that the material NiO is the charge-transfer insulator, which agrees with the spectroscopy data. The comparison between the charge density of LSDA (not considering U) and that of LSDA+U (considering U) demonstrates that the trend of ionic crystal for NiO is obvious.     

Effect of copper and cobalt impurities on the electronic structure and optical spectra of the intermetallic compound PrNi5

The electronic structure and optical properties of the intermetallic compound PrNi₅ and their evolution during the substitution of copper or cobalt atoms for nickel atoms have been investigated. The band spectra of the studied compounds have been calculated in the local spin density approximation corrected to account for strong electron-electron interactions in the 4f shell of the rare-earth ion (LSDA + U method). The dispersion relations of the optical conductivity in the interband light absorption region have been interpreted using the results of calculations of the electron density of states.     

First principles study of half-metallic ferromagnetism in Zn1−xEuxS

Density functional theory calculations by using both generalized gradient approximation (GGA) method and the GGA with considering strong correlation effect (GGA+U) for various Eu concentrations x (=0.00, 0.25, 0.50, and 0.75). It is found that after the Europium incorporation, a new localized band appears between the valence and conduction bands, which corresponds to the majority spin of Eu-4f states, the strong correlation effects is very important for the 4f orbit of the Eu atom in ZnEuS. We find that Zn_1−xEu_xS exhibits a half-metallic characteristic, and the ferromagnetic state is more favorable in energy than the antiferromagnetic state. Structural properties are determined from the total energy calculations, and we discuss the electronic structures, total and partial densities of states and local moments.     

Electronic structure of Gd-doped MgO

The electronic structure of Gd-doped MgO is investigated using the LSDA+U (local spin density approximation with U-correction) method and compared with the MgO structure. The total density of states obtained accounting for the correlation effects in the 4f shell of gadolinium is found to be formed by the oxygen 2p states at the valence band and the 4f gadolinium occupied states, while the conduction band is represented by a mixture of empty electronic states. Magnetic properties of the calculated Gd-doped MgO are found to be formed solely by the Gd-4f-magnetic moment of about 7μ_B, in good agreement with recent experimental results suggesting a ferromagnetic coupling of the local magnetic moments induced by Gd.     

NMR and magnetic susceptibility of the intermetallic pseudo-binary compounds Ce1−xRxAl3 with R=Gd,Tb and Er

The NMR and magnetic susceptibility of the intermetallic pseudo-binary compounds Ce_1?xGd_xAl₃ (x=0·01; 0·03; 0·05; 0·07), Ce_0·95Tb_0·05Al₃ and Ce_0·975Er_0·025Al₃ were investigated. The susceptibility is given by the sum of a temperature independent term and a Curie-Weiss one. The last one results from the contribution of the localized free-ion magnetic moments of all the rare-earth ions which are also responsible for the strong temperature dependent Knight shifts of the NMR lines of ²⁷Al nuclei via the exchange polarization of the conduction electrons. The ²⁷Al NMR spectra exhibit besides the line due to Al sites surrounded in the first coordination sphere as in CeAl₃ a second peak with a lower Knight shift due to Al nuclei positioned in the vicinity of a Gd, Tb or Er ion.     

Electronic structure of the TbMn<Subscript>0.33</Subscript>Ge<Subscript>2</Subscript> compound: Band calculation and optical experiment

The results of the investigation of the electronic structure and optical properties of the TbMn_0.33Ge₂ compound have been presented. The spin-polarized calculations of the band spectrum have been performed within the framework of the local spin density approximation (LSDA) with a correction for strong correlations in the 4f shell of the rare-earth ion (the LSDA + U method). The optical constants have been measured using the ellipsometric method and a number of spectral and electronic characteristics of the compound under investigation have been determined over a wide range of wavelengths. The interband part of the experimental dependence of the optical conductivity has been interpreted using the results of the calculation of the electron density of states.